Having to use Michelin's soft gravel tires on asphalt roads on this year's Rally Argentina has been the major talking point of this weekend's World Rally Championship round.
Ford's tire engineer George Black explains the challenge asked of the last two days.
Q. How much of a stress has it been on the soft tire to run on asphalt?
George Black: The biggest stress was actually trying to get the regulation sorted before this event started. We've known since December that these asphalt sections were coming, and I looked at the roads in January.
Yesterday's section, I wasn't concerned about the tire wear. Yes, the road was stupidly fast, but the cars came straight from the stage to service. My concern was for the second section, today's stretch of asphalt. You could not do that 21-kilometer stage [Las Jarillas] and then continue on the same tire and do another 60km of gravel stages on the same tire. We explained this to the organizers and they put another remote tire service in after that first stage this morning.
Q. That made everything more simple then?
GB: Yes and no. We had the opportunity to fit new or different tires after Las Jarillas, but we've had to really juggle with the tires because of those two extra fitment points – one this morning and one this afternoon. The original package was for 36 tires across shakedown and five fitment points [at service], but now we have seven fitment points and still only 36 tires – which is why we've been juggling the tires from the superspecial and shakedown.
For example, the tire package Jari-Matti [Latvala] will go out on for the first stage this afternoon came from shakedown on Thursday. It was a blessing in disguise that he had his broken gearbox on Thursday: it means he only did two runs at shakedown and we were able to save those tires. After that stage, Jari-Matti will have new tires for the rest of the afternoon.
But, I've got the likes of Ken Block, who took two spares every time yesterday and used those two spares as well and I'm now really starting to struggle to put the tire packages together for him for the first stage this afternoon.
Q. Some of the tires were coming back in looking very well worn, how would they have performed when they were effectively slicks?
GB: The grip on the asphalt wouldn't have been an issue because you're relying in compound grip and, as long as the conditions are dry, it would be OK. There was visible tread on some of the tires, but it was just a shadow. But on the Michelin you have two millimeters of compound rubber below the visible tread - and that last two millimetres actually lasts a remarkably long time.
When the road is clean, you don't need a lot of mechanical grip, you need compound grip. Obviously, that's quite different if you go off the clean line and onto the marbles, do that and you'll be all over the place.